JP4093885B2 - Radar device with anomaly detection function - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radar apparatus having an abnormality detection function, and more particularly to an FM-CW radar apparatus having a noise peak detection function.
[0002]
[Prior art]
In the FM-CW radar, a transmission wave that is frequency-modulated with a modulation signal in which a triangular wave consisting of an up-slope section and a down-slope section repeats is radiated forward, and a beat signal is generated between the reflected wave from the target and a part of the transmission wave. Is generated. When the frequency of the beat signal in the downward slope section is f _b (lower) and the frequency of the beat signal in the upward slope section is f _b (up), the beat frequency _fr and the target relative speed are caused by the distance to the target. The beat frequency f _{d to be} played is f _r = (f _b (lower) + f _b (upper)) / 2 (1)
f _d = (f _b (bottom) −f _b (top)) / 2 (2)
Is calculated by In addition, the target distance R and the target relative velocity V are
_{R = c · f r · T} / 4ΔF (3)
V = c · f _d / 2f _o (4)
(Where c: speed of light; T: period of triangular wave; ΔF: frequency modulation width (frequency shift width); f _o : center frequency)
Can be calculated with Therefore, the values of f _b (lower) and f _b (upper) corresponding to each target are determined from the peaks appearing in the spectrum of the beat signal on the frequency domain by Fourier transforming the beat signal, and (1) to (4) ), The distance to the target and the relative speed are determined.
[0003]
In FM-CW radar, if the output or input / output characteristics of elements such as an oscillator and a mixer have frequency characteristics (frequency dependence), the transmission wave and local signal are AM-modulated by FM modulation of the transmission wave. FM-AM conversion noise occurs. When this FM-AM conversion noise is included in the beat signal, it appears as a noise peak together with the peaks corresponding to the above-mentioned f _b (lower) and f _b (upper) in the Fourier transform result, reducing the signal detection accuracy, It may cause misrecognition. Therefore, it is necessary to detect a noise peak including a noise peak due to the FM-AM conversion noise by some means.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a radar apparatus having a noise peak detection function at low cost.
[0005]
[Means for Solving the Problems]
The first radar apparatus of the present invention comprises a measuring means for measuring a distance and a relative velocity with respect to a target by analyzing a peak appearing in a Fourier transform result of a frequency-modulated transmission wave and a beat signal of the reflected wave, Means for electrically or mechanically scanning the beam direction and means for identifying a noise peak based on a change in a Fourier transform result while the beam direction is scanned.
[0006]
The second radar apparatus of the present invention comprises a measuring means for measuring a distance and a relative velocity with respect to a target by analyzing a peak appearing in a Fourier transform result of a frequency-modulated transmission wave and a beat signal of the reflected wave, Means for substantially stopping frequency modulation of the transmitted wave, and means for discriminating a peak appearing at a frequency higher than a predetermined threshold as a noise peak while the frequency modulation is substantially stopped. .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of an FM-CW radar apparatus having an abnormality detection function according to an embodiment of the present invention.
[0008]
In FIG. 1, a modulation signal generator 10 generates a modulation signal in which a triangular wave consisting of an up-slope section and a down-slope section repeats in response to a command from the CPU 12. The voltage controlled oscillator 14 generates a transmission wave composed of a continuous signal frequency-modulated with this triangular wave. Part of the output of the voltage controlled oscillator 14 is branched by the branching means 16 and supplied to the receiving side, and most of the output is radiated forward from the antenna 18. The reflected wave reflected by the target existing ahead is received by the antenna 20 and mixed with a part of the transmission wave in the mixer 22 to generate a beat signal. The beat signal generated in the mixer 22 is amplified by the amplifier 24, unnecessary components are removed by the filter 26, converted into a digital signal by the A / D converter 28, and then supplied to the CPU 12. The CPU 12 performs a Fast Fourier Transform (FFT) operation on the digitized beat signal and converts it into the frequency domain, and then, for example, according to the above-described formulas (1) to (4), the distance R to each target and the relative velocity V Is calculated.
[0009]
In the FM-CW radar for in-vehicle use, as shown in FIG. 2, the direction of the transmitting antenna 18 and the receiving antenna 20 is electronically scanned by switches 30 and 32 or mechanically scanned by using a motor. Some can determine the lateral position X (= Rsin θ).
[0010]
In this case, as shown in FIG. 3, the normal peak due to reflection from the target exhibits a unique pattern that scans the angle θ, becomes maximum in the direction of the target, and decreases before and after that. On the other hand, at a noise peak caused by FM-AM conversion noise or the like, as shown in FIG. 4, the level of the peak becomes a substantially constant value regardless of the angle θ. Therefore, the threshold value is determined as shown in the figure, and a peak always having a level equal to or higher than the threshold value when the angle θ is scanned or a peak exceeding the threshold value at a certain rate or more is determined as a noise peak.
[0011]
This determination process can be realized as a software program to be executed by the CPU 12 (FIG. 1).
[0012]
The result of the FFT processing is output as a complex number composed of a real part (Re) and an imaginary part (Im), the level value is represented by √ (Re ² + Im ² ), and the phase value is represented by tan ⁻¹ (Im / Re). Is calculated. As described above, instead of determining the noise peak as the level does not substantially change when the angle θ is scanned, the phase at the frequency of the peak does not substantially change even when the angle θ is scanned. You may make it determine with a noise peak.
[0013]
In particular, when the focus is on the detection of FM-AM conversion noise, the FM-AM conversion noise appears in a specific region at a low frequency, and therefore only the peak appearing in such a specific region may be determined. In addition, when the gain of the amplifier in such a specific area is set to be low during normal use, it is possible to make a highly accurate determination by increasing the gain in that area or the entire area as compared with the normal gain. This gain change can be realized by switching the amplifier to be used or by changing the setting of the AGC amplifier. Alternatively, the detection accuracy of the abnormal peak is improved by setting the threshold value for detecting the peak in the spectrum to be lower than the normal time at the time of abnormality determination. When the level of the peak detected on the spectrum is high, the level may be saturated and the peak based on the target may not change, but in that case, the gain of the amplifier is lowered.
[0014]
When a noise peak is detected by the above determination processing, detection processing is performed several times thereafter (several scans), and when a noise peak is detected for an arbitrary number of times, the peak is determined as noise. It is desirable.
[0015]
When a noise peak is detected by the determination processing, detection processing is performed several times (for several scans), and when the detection frequency is larger than an arbitrary value, the peak noise may be determined.
[0016]
In normal processing, when a peak exists in a frequency band equivalent to the peak determined as noise in the noise determination processing, the peak may be determined as noise.
[0017]
When the FM modulation is stopped by the instruction of the modulation signal generator 10 (FIGS. 1 and 4) from the CPU 12 or the modulation width is made extremely small, only the peak of the Doppler frequency based on the relative speed appears on the spectrum of the Fourier transform result. Appear. Even if the upper limit of the relative speed is estimated to be 400 km / h, the frequency is 40 kHz or less. Therefore, at this time, for example, a peak existing in a region of 50 kHz or higher can be regarded as a noise peak. In this way, noise peaks other than FM-AM conversion noise can be detected.
[0018]
【The invention's effect】
As described above, according to the present invention, a radar apparatus having a noise peak detection function is provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an FM-CW radar to which the present invention is applied.
FIG. 2 is a diagram showing an FM-CW radar having a function of electronic scanning in a radial direction.
FIG. 3 is a diagram showing a normal peak when scanning in the radiation direction.
FIG. 4 is a diagram showing an abnormal peak when scanning in the radiation direction.

Claims (11)

A measuring means for measuring a distance and a relative velocity with respect to a target by analyzing a peak appearing in a Fourier transform result of a beat signal of the frequency-modulated transmission wave and its reflected wave;
Means for electrically or mechanically scanning the beam direction;
In the Fourier transform results between the beam direction is scanned by determining the peak peak or the phase does not change more than a threshold level is always or a percentage above a threshold or more as noise peaks, FM-AM A radar apparatus having an abnormality detection function, comprising: means for identifying a noise peak that appears as a peak in a Fourier transform result by conversion noise.   The radar apparatus according to claim 1, wherein the noise peak identification unit sets a predetermined frequency region as a noise peak determination target.   3. The radar device according to claim 1, wherein the noise peak identification unit determines a noise peak by changing an amplifier characteristic in a predetermined frequency region. 4.   The radar apparatus according to claim 3, wherein the noise peak identification unit determines a noise peak by changing an amplifier characteristic so that an amplifier gain is different.   The radar apparatus according to any one of claims 1 to 4, wherein the noise peak identification means determines a noise peak by changing a threshold value for peak detection.   The radar apparatus according to claim 3, wherein the noise peak identification unit changes an amplifier characteristic by switching an amplifier to be used.   The radar apparatus according to claim 3 or 4, wherein the complex peak identifying means changes an amplifier characteristic by changing an AGC amplifier setting.   The radar apparatus according to claim 1, wherein the noise peak identification unit determines a noise peak by lowering a gain of an amplifier when a level of a detected peak is higher than a predetermined value.   The radar apparatus according to any one of claims 1 to 8, wherein the noise peak identifying means finally determines a peak determined to be a noise peak continuously a plurality of times as a noise peak.   The radar apparatus according to any one of claims 1 to 8, wherein the noise peak identifying means finally determines a peak determined to be a noise peak at a predetermined frequency or more as a noise peak.   The radar device according to any one of claims 1 to 10, wherein the noise peak identifying unit determines that a peak existing in a frequency band equivalent to a peak determined to be a noise peak is a noise peak.

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